Plot

One stormy day, the Gauls — with the exception of Getafix, who is at his annual druid meeting — are huddled in the chief's hut, fearing for their lives. But then, a man enters the hut in a burst of lightning - it is a soothsayer, who promptly proceeds to see the future for our superstitious Gauls. He predicts that "when the storm is over, the weather will improve." But not all are impressed; Asterix alone dares question the qualities of this soothsayer, who is in fact a fraud.

Although Asterix can see this, not everyone is convinced, most notably Impedimenta, the chief's wife. Partly out of superstition and partly out of personal ambition, she convinces the soothsayer (known also by the name "Prolix") to remain in official hiding near the village, where she and the other villagers may question him at will. The only two whom she will not permit into the forest are Asterix and Obelix. Obelix in particular has a grudge against the soothsayer, who has threatened to kill Dogmatix in order to examine his guts for predictions of the future.

When Obelix finally thwarts Impedimenta and enters the forest, he finds Prolix there and chases him up a tree. When he threatens to uproot it, Prolix puts him off by claiming to see a vision of a beautiful woman who loves warriors matching Obelix' description. Obelix returns to the village and almost instantly falls for Mrs. Geriatrix.

Prolix meanwhile is arrested by a strictly rule-abiding Roman Optio (a senior officer). The Optio brings Prolix before the Centurion, who decides to make use of the imposter's persuasive voice.

Back in the forest Impedimenta and Asterix have within moments of each other discovered the absence of the soothsayer, causing consternation among the villagers who were told by the soothsayer that the gods would put a curse on them if anything untowards happened to him. Being that Obelix has been beguiled by Prolix's ironically accurate description of Mrs. Geriatrix (not mentioned by name), Asterix finds himself standing alone. Prolix returns at that moment, claiming dramatically that soon the air in the village will become polluted by a divine curse. Terrified, most of the villagers leave their home, to wait on a nearby island for the curse to run its course, as if it were a quarantined virus. Asterix, Obelix, and Dogmatix stay behind.

The Romans soon arrive to investigate the village, while the Gauls hide in the local undergrowth. Unknown to either, Getafix has completed his conference (which seems to be a facsimile of a twentieth-century scientific conference) and returned. Hearing of the situation, he concocts a witty plan by which to drive out the Romans and teach the villagers a lesson. Using a number of unidentified ingredients in his cauldron, the Druid literally raises such a stink that even the powerful Obelix is affected. The fumes spread to the village, expelling the Romans, Prolix, and Cacofonix the Bard who had sneaked back to find his lyre.

Prolix is baffled: the seeming fulfillment of his prediction has set him to wondering if he is becoming a real soothsayer. On the other hand, the appearance of the foul air has cemented the Centurion's faith in his oracle. He sends word to Caesar that all of Gaul is now conquered ("All?" "All."). But, like Crismus Bonus of Asterix the Gaul, he begins to desire the Imperial Throne for himself. To pass the time, therefore, he has the soothsayer tell him exaggerated stories of the luxuries emperors enjoy.

Meanwhile, Getafix joins the other villagers on the island to explain the Truth. Here we see a reference to the priestly role of the Druid, when Vitalstatistix begs Getafix to "appease the anger of the Gods, which has fallen upon our poor village." To which Getafix replies "Nonsense!" and proceeds to demonstrate what is really going on.

Inspired by this, the villagers go home, while the Romans deal with their own problems. The Optio is himself confused, because even though the Centurion is convinced that Prolix is a genuine soothsayer, the Optio's own observations tell him otherwise. Though upright and law-enforcing, he is not intellectual and finds himself thoroughly perplexed by the simplest of contradictions. Even his inferior officers regard him as an "idiot".

In the village, trouble is still present. Impedimenta and her fellow women are not convinced that Prolix was a cheat, partly because he only foretold pleasant things for them, such as a business partnership between Vitalstatistix and Impedimenta's brother Homeopathix, each of whom considers the other an arrogant dope.

Asterix has an idea; they might give the soothsayer a surprise, to prove that his predictions are not genuine. The surprise is quite simple: the Gaulish men and women will attack the Roman camp together. The plan is successful: the Gauls arrive at the camp and Prolix admits that he had no idea that they were coming. This convinces Impedimenta who beats the Centurion and the soothsayer with a rolling pin, causing her husband Vitalstatistix to look on her with an almost patronizing pride.

Returning to the village, the Gauls meet an envoy of Caesar's who has come to check on the Centurion's claim that the village is conquered. They beat him and his escort up.

The envoy, Bulbus Crocus, goes to the camp and faces the Centurion: "AND LOOK WHAT YOUR CONQUERED GAULS DID TO US, BY JUPITER!" He reduces the centurion to a common soldier, and, when the ex-centurion reflexively tries to give the Optio an order, the Optio rebukes him for his tone to a superior officer and orders him to sweep out the camp alone.

Prolix, who has been taking a lot of yelling from the now-ex Centurion over being a fraud, leaves the camp swearing to give up soothsaying at the risk of having the sky fall on his head, whereupon Rain-God, Taranis, sends down a thunderstorm.

The Gaulish village, however, is soon at peace, enjoying themselves for the present and not worrying about the future - with the exception of Cacofonix, who still dreams about being a famous singer.

Adaptations

An animated film bearing the title Asterix and the Big Fight was released in 1989, however although it contains elements from that album, it is actually more an adaptation of this book. Part of the plot was also used in the first live action Asterix film, Asterix and Obelix vs Caesar.